Protective means for transmission-lines.



G. J. D. CENTERWALL.

PROTECTIVE MEANS FOR TRANSMKSSION LINES.

APPLICATION FILED APR. 19, 1912.

1 04,407. Patented Nov. 14, 1916.

/ 5 5 8 5 F/ a 5 2 l/ 4 Hz; 6. F/q] WITNESSES: S E T m/ I W B 2 MATTORNEY UNITED STATES PATENT OFFICE.

GEORGE J'. D. CENTERWALL, STOCKHOLM, SWEDEN.

PROTECTIVE MEANS FOR TRANSMISSION-LINES.

Application filed April 19, 1812. serial No. 691,846.

To all whom it may concern Be it known that I, GEORGE J. D. CENTER-WALL, a subject of the King of Sweden, and a resident of Stockholm, inSweden, have invented a new and useful Improvement in Protective Meansfor Transmission-Lines, of which the following is a specification.

My invention relates to electrical systems of distribution andtransmission and it has particular reference to protective devices foruse in connection with high voltage transmission systems for the purposeof preventing excessive peak voltages, and line surges.

The object of my invention is to provide a system of the above-indicatedcharacter which shall be simple in arrangement, effective and reliablein operation and shall embody adequate means for preventing momentaryexcessive voltages and disturbances.

It is well known in the art that considerable energy is dissipated insilent electrical discharges, known as corona, which are effected atvery high potentials, and also that high-potential disturbances may beprevented to some extent when a system is working at the so-calledcorona voltage.

Abnormal voltages and surges in hightension transmission systems usuallyresult from electric charges, traveling along the line wires in aboutthe same way as waves of sound in a tube, being reflected and damped inaccordance with similar laws. Reflection of the electric waves takesplace when the waves encounter devices containing inductance andcapacity in other proportions than the line itself, but the damping ofthe waves can be eflected only as a result of dissipation or loss ofenergy.

The simplest way of dissipating energy from static Waves is throughohmic resistance. Such resistance cannot however be directly connectedbetween the wires or to ground for the reason that, with such anarrangement, a considerable loss of energy would be sustainedcontinually, even at normal voltage. Consequently, it is necessary tohave a spark gap in series with the energ consuming resistance. It isimpossible, however, to disconnect the damping resistance immediatelywhen normal conditions are restored, as a power are will follow in thepath of the original static discharge, which will be maintained for aperiod many times longer than thetime which it takes for the wave ordischarge to pass. For this rea a heat capacity suflicient to.accommodate an amount of energy very much larger than that of thetraveling waves or surges. Different apparatus, have been employed forthe purpose of rupturing the current through the resistance at thecritical moment after the static discharge has passed, among the mostimportant devices of which is the electrolytic lightning arrester.

In my invention, therefore, I propose to utilize the corona dischargesfor dissipating the excessive energy in case of abnormal surges andvoltage waves. Corona produces an ionization and splitting-up of the airmolecules around the wires and is accompanied by a dissipation of energyin connection with chemical processes in the formation of ozone andnitric acid. Part of the energy is also directly converted into lightand heat. It is evident, that this is an entirely different way ofdissipating energy from the voltage waves and oscillations than by meansof ohmic resistance.

A study of the laws of corona shows, that the energy loss starts at apredetermined voltage which depends only on the voltage gradient in theair surrounding the wires. This voltage can be regulated at will bychanging the size or the distance between the line conductors. In somecases, systems working at very high voltage will, to some extent,protect themselves against surges, z'. c. the oscillations will besomewhat more damped than through the resistance of the line wiresalone. In most cases, however, it will be necessary to make specialarrangements, in order to carry off or dissipate the desired amount ofenergy in corona discharges.

It is my purpose, therefore, to provide means for causing the formationof corona at a predetermined voltage, whereby the desired results areaccomplished, and I attain these ends by employing, either directly orindirectly, with the transmission circuits,

conductors of relatively small section or of peculiar shapes that areparticularly conducive to the formation of corona. By suitably choosingthe size of these small protecting conductors or the particular shapesthereof, it is evident'that the formation of corona maybe effected atany predetermined voltage, whereby energy is dissipated and excessiveand dangerous surges are prevented.

son, it is necessary to, provide resistances. of" My invention may'bestbe understood by Specification of Letters Patent. P t t N 14, 191

reference to the accompanying drawings, in which Figure l is adiagrammatic view of a portion of a transmission system embodying myinvention. Figs. 2, 3, 4 and 5 are views similar to Fig. .1, showingvarious modifications which embody my invention, and Figs. 6 and 7 aresectional views of conductors of peculiar shapes that are particularlyconducive to the formation of corona.

Referring to Fig. 1 of the drawings, a plurality of substations 1 and 2,or the like, are connected by a transmission line 3 which is here shown,for convenience, as a single conductor but which may comprise severalconductors, as is the usual practice. At varying intervals, protectingconductors 4 are inserted in series with the transmission circuit 3, forthe purpose of facilitating the formation of corona and thus preventingexcessive voltages. These protecting conductors 4 may be of relativelysmall section in comparison with that of the conductor which constitutesthe transmission line 3 or may be of one of the shapes shown in Figs. 6and 7, or mayhave other suitable shapes that are peculiarly conducive tothe production of corona.

At the right-hand end of the transmission circuit 3, a plurality ofprotecting conductors 4 are shown as being connected in multiple inorder that the resistance of the transmission line may not be increased.

If the material of which the transmission line is composed is aluminum,a single protecting conductor of copper may be included in seriestherewith without increasing the normal resistance of the line, byreason of the greater conductivity of the copper conductor. Also. insome cases, in order to suppress rapid electrical changes, iron wire, orwire covered with iron or nickel may be employed.

In the operation of the system, if the voltage rises above theparticular value for which the protecting wires 4 are designed, it isevident that the formation of corona is effected thereon which serves toprevent any surges or momentary line disturbances.

In Fig. 2, the transmission line 3, which connects the several stations1 and 2. is provided with a protecting wire 4 similar to thathereinbefore described, said wire being connected in parallel wit-h aportion of the transmission line.

In Fig. 3, the stations 1 and 2 are connected by the transmission line 3which includes a choke coil 5 in accordance with usual practice. Aprotecting wire 4 is connected to the transmission line 3 at one end andan auxiliary wire 6 is disposed in proximity thereto and is connected inseries with resistance 7 to ground. By reason of this and by properlychoosing the distance between conductors 4 and 6, as well as the valueof the resistance 7, it is possible to cause the formation of corona atany predetermined voltage.

Another form of protective means embodying my invention is shown at thelefthand end of the transmission line 3 which comprises a plurality ofprotective conductors 4 which are segregated, one from the other, bymeans of suitable spark gaps 8, and which are decreased in sectionprogressively from the extreme left protecting conductor 4 which isconnected to the transmission circuit 3. Vith this arrangement ofcircuits, the various protecting conductors 4 are successively broughtinto circuit in accordance with line conditions, whereby a considerableamount of energy may be dissipated. Hence, this arrangement is of greatprotective value.

- Referring to Fig. 4, the transmission circuit 3, which connects thestations 1 and 2, is provided with a protecting wire 4 at one endthereof and, in connection with the wire 4 is an oscillation circuit 9which includes a condenser 10, an inductance 11 and a spark gap 8, saidoscillation circuit being grounded through a suitable resistance 7. Bymeans of this arrangement, the formation of corona upon the protectingconductor 4 mav be greatly facilitated by effecting changes ordistortions of the alternating current waves by means of dischargesacross the spark gap 8. This result is accomplished by suitableadjustments of the condenser 10 and the inductance 11 whereby resonantconditions are obtained. Discharges across the spark gap 8 are effectedwhich correspond to the peak of each high-voltage wave, and this actiontends to permit the voltage of the oscillation circuit to build up to ahigh value, at which corona is formed, which serves to protect thesystem from excessive surges or line disturbances.

Referring to Fi 5, the stations 1 and 2 are connected by a transmissionline 3 of low or moderate potential which is much less than that atwhich corona is formed.

In order to perform the function of a protective device, in connect-ionwith a sys tem of comparatively low voltage, the protective wire 4 maybe associated with the transmission line 3 through a transformer 12, thewindings 13 and 14 of which are adapted to step up the normal voltage ofthe system to a high voltage, which is increased sufficiently to producecorona discharges upon the conductor 4 in case excessive conditionsobtain upon the transmission circuit.

For illustrative purposes, I have shown and described several particulararrangements of circuits embodying my invention, but it will beunderstood that various modifications may be effected therein withoutdeparting from the spirit and scope of my invention, and I intend tocover such variations in the appended claims.

I claim as my invention:

1. In an electrical power-transmission system, the combination with aline-conductor that is not conducive to the formation of coronathereupon under operating voltages and which is subject to abnormalhighpotential disturbances, of means influenced by the potentialsobtaining on said line-conductor for dissipating, through the formationof corona, the excess energy only that results from the abnormaldisturbances.

2. In an electrical power-transmissi on system, the combination with aline-conductor which is so formed as to be non-conducive to theformation of corona under operating conditions and is subject toabnormal highpotential disturbances, of means influenced by thepotentials impressed on said lineconductor for dissipating energy,through the formation of corona, only during the time that the abnormaldisturbances maintain the potential of said line-conduc torsubstantially above its working potential.

3. In an electrical power-transmission system, the combination with aline-conductor that is not conducive to the formation of coronadischarges under operating conditions and that is subject to transienthighvoltage disturbances, of means associated with said line conductorand comprising a protecting conductor that is under the influence of theabnormal potentials obtaining on the line-conductor and is effectivelyinsulated from ground for damping said disturbances by generating coronadischarges.

4. In an electrical power-transmission system, the combination with aline-conductor of relatively large cross-sectional area which isnon-conducive to the formation of corona discharges thereupon underoperating conditions, of a protective conductor from which discharges toground are precluded and which is conducive to the formation of coronadischarges when subjected to potentials above a predetermined value andwhich is influenced'by the potentials obtaining upon the line conductorfor dissipating through corona discharges the energy of high-potentialdisturbances only that may be impressed on said line-conductor.

5. In an electrical power-transmission system, the combination with aline conductor which is not conducive to the formation of coronadischarges under operating conditions and is subject to electricaldisturbances, of a second conductor which is conducive to the formationof corona discharges when subjected to potentials above a predeterminedvalue that is below the value at which corona discharges will emanatefrom said line conductor, said second conductor being influenced by thepotentials obtaining on said line conductor, whereby the line conductormay be relieved, through the corona discharges emanating from saidsecond conductor, of only the excess energy resulting from thehigh-potential disturbances.

6. In an electrical power-transmission sys- V tem, the combination witha line conductor which is not conducive to the formation of coronadischarges under operating conditions and'is subject to electricaldisturbances, of at least one conductor of relatively smallcross-sectional area which is conducive to the formation of coronadischarges when subjected to voltages above a predetermined value thatis below the value at which corona may form on said line conductor, saidsec ond conductor being influenced by the potentials obtaining on saidline conductor in order to relieve the line conductor of the i excessenergy resulting from the disturbances impressed thereupon throughcorona discharges emanating from said second conductor.

7. The method of protecting an electrical transmission system whichconsists in discharging therefrom the eXcess energy resulting fromabnormal disturbances that may be impressed upon the system by theproduction of corona emanations in a portion of the system only when thevoltage of the system is raised above a predetermined value.

8. The method of protecting an electrical transmission system, theconductors of which are not conducive to the formation of coronaemanations under operating voltages, which consists in discharging from'the system only the excess energy that results from abnormaldisturbances occurring in the system by the production of corona GEORGEJ. D. CENTERVVALL.

W'itnessesz' DRETA PRIM, FREDR. NORDSJO.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents,

Washington, I). C. a I

